The Russian deal includes taking back the spent fuel, which reduces the chances that the Iranians could divert some percentage of the nuclear materials into their weapons programs.
Iran hoped to get the reactor up and running as the reactor was fueled, but now comes word that all of the fuel will need to be removed so as to conduct additional tests and carry out modifications.
Iran will remove the fuel from the reactor of a Russian-built nuclear power plant in the southern city of Bushehr, a top official said on Saturday, citing technical advice from Moscow.
The plant, which has seen a roller-coaster ride since its construction began in the 1970s, was scheduled to generate electricity from April 9, and the latest development signals a likely delay in achieving that aim.
"Based on the recommendation of Russia, which is in charge of completing the Bushehr atomic power plant, the fuel inside the reactor core will be taken out for a while to conduct some experiments and technical work," Iran's envoy to the UN atomic watchdog, Ali Asghar Soltanieh, told the ISNA news agency.
"After the experiments, it will again be installed in the core of the reactor." He did not specify when the experiments would be completed.
Iran had started loading the fuel into the plant on August 21, which Moscow at that time said was the "physical launch" of the facility.
In January, Iran's former atomic chief Ali Akbar Salehi said the plant would be ready to generate electricity on April 9 after operations began on November 27.
The decision to remove the fuel, also supplied by Russia, is the latest development in the more than three-decade old history of the plant, which was first launched by the US-backed shah using contractors from German company Siemens.